1. Field of the Invention
The embodiment discussed herein is directed to a speed change control apparatus for a work vehicle.
2. Description of the Related Art
Conventionally, there have been speed change control apparatuses of work vehicles such as tractors that detect movements of a speed change pedal by a pedal sensor and control output of an engine and a hydraulic continuously variable speed transmission (HST: hydro static transmission) based on a detection value to adjust a travel speed. The hydraulic continuously variable speed transmission includes a variable displacement hydraulic pump and a fixed displacement hydraulic motor, rotates a trunnion shaft coupled to a movable swash plate of the hydraulic motor, and changes the inclination of the movable swash plate, whereby the rotation of the hydraulic motor can be changed.
Japanese Patent Application Laid-open No. 2013-7470 discloses a technique that examines a relation between a drive current and the number of revolutions of an output shaft of a hydraulic continuously variable speed transmission in an adjustment mode and sets a current value at which the output shaft of the hydraulic continuously variable speed transmission starts to move and a current value at which the number of revolutions of the output shaft is maximized for each body, for example.
Even when the hydraulic continuously variable speed transmission, an interlocking mechanism with a speed change pedal coupled to this hydraulic continuously variable speed transmission in an interlocked manner, or the like differs from one work vehicle's body to another, the speed change control apparatus can perform control so as to give a certain set speed at a certain turning position of the speed change pedal. Consequently, a travel speed by the hydraulic continuously variable speed transmission can be prevented from varying from one body to another.
Literature related to the conventional technique is Japanese Patent Application Laid-open No. 2013-7470, for example.
However, the speed change control apparatus for the work vehicle disclosed in Japanese Patent Application Laid-open No. 2013-7470 can sometimes give a nonlinear change in a trunnion shaft angle of the hydraulic continuously variable speed transmission relative to a depressing amount of the speed change pedal in design in which a turning support of the speed change pedal and a terming support of the pedal sensor are offset from each other, for example. In other words, the technique of Japanese Patent Application Laid-open No. 2013-7470 can cause an operator to feel uneasy with an operation feeling of the speed change pedal and still has room for improvement in the operation feeling.